604 FORTIF 
dually diminifh three feet in height from the rampart of 
that place ; thus if the town ramparts are eighceen feet 
high, the rampart of the next outwork is fifteen feet 
high, that of the work next advanced is twelve feet, and 
fo on; thus the more advanced outwork is commanded 
by that next within it. 3. The flanked angle of an out. 
■work ought not to be lefs than fixty degrees. 4. Each 
outwork ihould be furround'e <3 with a ditch communicating 
■with the fofs of the town. When all the ditches can be 
filled with water, they ought to be equally deep ; but 
when that cannot be obtained, the ditch.es of outworks 
fhould be fhallower than that of the town ; by which 
means the.front of the outworks will be better defended 
from the parts which flank them. Thefe ditches are 
■'ufually from about twenty to twenty-four yards broad, 
and rounded to that breadth before the faliant angles, 
with the counterfcarps parallel to the faces or outlines of 
the work they encompals. 5. The parapets of outworks 
are to be equally ftrong and high with thofe of the town, 
as they are to be cannon-proof, and to cover the troops 
deltine’d for their defence. It is ufual to make the para¬ 
pets of outworks of about eighteen feet thick, fix feet 
high, with a foot-bank four feet lower than the crown of 
the parapet; and the walk of the rampart about feven or 
eight yards broad, with a flope within of about half its 
height. 
The ravelin is a work cotiftrufted before a curtain, as 
fliewn in the engraving at fig. 14, 15, 16, and 17, ferving 
to cover that work and the adjoining flanks from the 
«lireft fire of an enemy. It is compofed of two faces, 
AB, AC, fig. 14, and the two demigorges, pB, p C, taken 
on the counterfcarp.— To conjlrutl a ravelin. In a line 
drawn at right angles to the curtain through its middle, 
take the capital p A equal to about one hundred yards, 
and draw the faces AB, AC, directed to points in the 
faces of the next baftions, about ten yards diftant from 
M, the angle of the Ihoulder. Project a rampart of about 
twenty yards, and a parapet of about fix yards ; and be¬ 
fore the faces put a fofs of about twenty-four yards wide, 
rounded before the faliant angle A ; alfo annex ramps in 
■the flope of the rampart, and, if requilite, conftruft a 
barbet in the faliant angle. The gorge of the ravelin, 
or the part next the town, is left without any rampart; 
becaufe the enemy cannot attack it there ; and alfo, that 
it may be entirely commanded from the ramparts of the 
town. 
It is proper to make a ravelin before every curtain, 
becaufe the flanks are by this means covered from the 
enemy, and cannot be ruined before he is maker of the 
■ravelin; but without which, he would have it in his 
power to batter the flanks from the counterfcarp, both 
from before the curtain and the face of the baftion ; the 
latter being the only place he can do it from, when a 
ravelin is interpofed, of which he is not mailer. The 
difficulty of erecting a battery on the head of the glacis 
again!! the face of a baftion, is alfo too great to be under¬ 
taken, while the place is defended by the whole fire of 
the adjacent face of the ravelin : and therefore the be- 
fiegers can make little imprellion on the flanks before 
they have taken the ravelin; Inch works therefore greatly 
augment the defence of a town. 
As the face and fofs of a ravelin is defended by the op- 
polite baftion, the faces of the ravelin fhould be directed 
fonrewhat within the angle of the lhoulder, at leaft as 
much as the breadth of the parapet and foot-bank of the 
flank : for by this conftruftion they cover the flanks 
more effectually ; which is one of the principal objefts, 
fince the flanks are of the greateft importance, and to be 
prelerved tire longed. In wet folfes, where the troops 
pafs from the town to the ravelin in boats, it is proper 
to make a kind of harbour in the gorge of the ravelin, 
where the boats may fecurely lie, covered from the fire 
cf the enemy. This may be done by making an excava¬ 
tion limited by an arc deferibed from A, fig. 15, the 
angle of the counterfcarp, with a radius of about twenty 
CATION. 
yards'. In dry folfes, it is proper to have either ramps 
or flairs in the gorge of the ravelin, to preferve a free 
communication, fhould the bridges be broken bv the 
enemy. 
In fome ravelins, as at fig. 16, there is conftrufted a 
kind of redoubt, or keep, which is a frnall work fimilar to 
the ravelin, with a ditch, ten or twelve yards wide. The 
capital may be thirty or forty yards ; and the work co¬ 
vered in the faces by a wall two feet thick, furniffied with 
loop-holes for the mulketry to fire through. This keep 
lerves to fecure a retreat for the troops who defend the 
ravelin, and on this account the defence of the breach in 
the ravelin may be more obftinately refilled ; for even 
when the befieged are obliged to give way to a fuperior 
force, they may retire into the keep, and prevent the 
enemy from making a lodgment in the outward part of 
ravelin, or at leaft greatly obftruft it ; and cannot be 
driven from this work until the enemy has ereCted a bat¬ 
tery, and brought cannon on the ravelin to batter the 
keep. The conftruftion may be otherwife made by taking 
the diftance B A, equal to about twenty- yards, on the 
gorge of the ravelin, and out of the reft forming the keep 
with its fofs; the (carp and counterfcarp being drawn 
parallel to the faces of the ravelin, the two fronts of 
which form a work covering the keep, and is ufually 
called the counter-guard. 
The ravelins, commonly called half-moons, have fome- 
times their corners at B and C, fig. 14, cut oft', either 
parallel to the capital p A, or at right angles to the fofs, 
making a kind of flank, of about twelve yards long, with 
its rampart and parapet. This ferves to give a more 
direft fire along the covered-way, which is meant more 
particularly to be defended ; but then it partly lays open 
the flanks, which the ravelins were originally intended 
to cover. 
The celebrated general Coehorn, in the ravelins which 
lie built at Bergen-op-Zoom, invented a very good de¬ 
fence for the covered-way before the faces of the baftions, 
by making retired flanks in the breafts of the ravelin, 
where one or two cannon' may be placed, equally fecure 
from the enemy’s fire, as thole placed behind the orillou 
of a baftion. Thefe malked cannon in the ravelin feem 
to have been intended for the defence of the covered-way 
on the laft emergency; as thole in the baftion are for the 
defence of the breach, when the befiegers attempt to ftorm. 
But the covered cannon in the ravelin appear to have this 
preference; that, as towns are not ufually given up until 
the enemy is mailer of the covered-way, the fecreted guns 
in the ravelin have often an opportunity of being effectu¬ 
ally employed; whereas the guns covered by the orillons 
are very rarely ufed, becaufe there are few garrilons which 
Hand long the ftorm of the breach in a baftion. . 
Coehorn’s ravelins may be thus projected : In the gorge 
of the ravelin take ab, fig. 17, equal to about twenty yards, 
draw the flank be at right angles to ab, make be equal to 
about twelve or fourteen yards, and draw the cover cd 
parallel to ab. To the flank be annex a rampart, parapet, 
embrafures, and ramp ; and to prevent thefe flanks being 
raked by the enemy’sbatteries, particularly by the ricochet 
or bounding (hot, there may be made a traverfe about ten 
feet thick acrofs the top of the flank at c, with a fmall 
mine under it, to blow up the traverfe whenever the be¬ 
fieged are obliged to quit the ravelin, left it Ihould lerve 
to cover the alfailants from the fire of the town. Coehorn 
alfo made flanks at the corners d of the ravelin, which 
may be conftrufted by taking an equal to ten yards, and 
drawing ne parallel to be , meeting cd in d\ then de is the 
flank required. 
The counterguard, is a work generally ferving to cover 
a baftion : it is compofed of two faces, forming a faliant 
angle before the flanked angle of a baftion. The mode 
of conftrufting it is thus : Having deferibed the ravelins, 
and drawn their folfes, in the counterfcarp of the ravelin, 
take ab, fig. j8, equal to about twenty-four yards, and 
draw the face be parallel to the counterfcarp of the fofs 
before 
